The present invention is a process for the purification of halosilanes. The process consists of contacting a mixture comprising a halosilane and a hydrocarbon with an adsorbent selective for the hydrocarbon, thereby reducing the hydrocarbon content of the mixture. The present process is particularly useful for removing hydrocarbon contaminates from chlorosilanes, where the hydrocarbon contaminates have a boiling point similar to that of the chlorosilanes.
Hydrocarbon contaminates in halosilanes can create quality problems such as undesirable odor and color not only in the halosilanes, but in products made from the halosilanes. In addition, in cyclic processes using halosilanes as feed, where unreacted materials are being recovered and fed back to the process, hydrocarbons can build up in the process leading to a decrease in process capacity and operational control. Often it is hard to remove these hydrocarbon contaminates from the halosilanes by standard processes such as distillation because of similar boiling points.
The present process is particularly useful for removing hydrocarbon contaminates from halosilanes prepared by the reaction of an organohalide with silicon metalloid in the presence of a suitable catalyst, as was originally described by Rochow, U.S. Pat. No. 2,380,995, issued Aug. 7, 1945.
The use of adsorbents to recover hydrocarbons from air and hydrocarbon mixtures generated during the production and transfer of petroleum products is described, for example, in Quackenbush, U.S. Pat. No. 4,056,369, issued Nov. 1, 1977; McGill et al., U.S. Pat. No. 4,066,423, issued Jan. 3, 1978; Dinsmore et al., U.S. Pat. No. 4,462,811, issued Jul. 31, 1984; and Tuttle, U.S. Pat. No. 4,338,101, issued Jul. 6, 1982. A typical adsorbent used to recover the hydrocarbons is activated carbon.
McGill, U.S. Pat. No. 4,305,734, issued Dec. 15, 1981, describes a process for recovering methane vented from industrial operations such as coal mines. The described process consists of passing a hydrocarbon-carrier gas mixture through an adsorbent bed capable of selectively adsorbing the hydrocarbon components from the mixture to produce a stream of substantially hydrocarbon-free carrier gas. McGill teaches the process is particularly useful for separating methane from air and for separating ethylene from air or nitrogen streams which vent from polyethylene manufacturing facilities. McGill teaches activated carbon as a typical adsorbent.
Sircar, U.S. Pat. No. 4,784,6712, issued Nov. 15, 1988, teaches that activated carbon can be used to remove hydrocarbons and halohydrocarbons from methane and carbon dioxide present in landfill gases.
Sacchetti et al., U.S. Pat. No. 4,421,532, issued Dec. 20, 1983, describes a process for recovering volatile organic substances from industrial waste gases. The process involves the passing of the waste gas through a bed of an adsorbent such as activated carbon, silica gel, alumina, or molecular sieve to remove volatile organic substances, and then regenerating the adsorbent bed by stripping with steam or a hot gas.
Zizka et al., Czech. Patent No. 89396, published Apr. 15, 1959, describes a process for the recovery of methyl chloride from the direct process for producing organochlorosilanes. In the process described by Zizka et al., the gaseous mixture resulting from the direct process is first treated with a dilute NaOH of KOH solution to remove hydrolyzable methylchlorosilanes. The treated gas is then contacted with activated carbon which adsorbs the methyl chloride. The methyl chloride is recovered from the activated carbon by thermal desorption, in some cases with simultaneous pressure reduction.
The present inventors have found that hydrocarbon contaminates present in halosilane liquids and gases can be reduced by contacting the halosilane liquid or gas with an adsorbent selective for the hydrocarbon. The described art does not recognize that adsorbents can selectively adsorb hydrocarbon contaminates from halosilane liquids and gases.